Ophthalmic perimeters



May 8, 1956 G. E. cox

OPHTHALMIC PERIMETERS 2 Sheets-Sheet l Filed May 6, 1952 .,---TIHHH ..1--.HT w

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George. [Jv d al May 8, 1956 G. E. cox, 2,744,441

OPHTHALMIC PERIMETERS Filed May 6, 1952 2 Sheets-Sheet 2 25a 31 /27b vlll L@ 5o HNI 5b 27a 3l 8 27a l' l if/Lnb tionally in any one of the countersinks that has been brought into register with the ball by rotation of the arc 2 with consequent rotation of the spindle 11 and disc 13.

Adjacent the outer face of the disc 13 the recess 1f accommodates a dial 19 which is held in place by means of a spring ring 20 engaged in a groove in the circular wall of the recess, and is marked with graduations corresponding to the angular distances between the countersinks 15 and the disc 13. To the end part of the spindle 11 projecting beyond the dial 19 there is applied a pointer 20 which is secured to the spindle by means of a spring clip 21. Thus, when the arc is rotated, with consequent rotation' of the spindle 11 and the disc 13 to bring any one of the countersinks 15 into a position in which it is engaged by the ball 16, the angular setting of the arc will be indicated by the position of the pointer 2G in relation to the graduations marked on the dial 19.

The dial 19 and pointer 20 are protected by a window 22 of suitable transparent material which is accommodated in the recess 1f and is held in place by means of a spring ring 23 engaged in a groove in the circular wall of the recess.

In the embodiment illustrated, there are provided eight countersinks 15 and as these are equidistantly spaced round a circle concentric with the axis of the bore 1d, the distance between any one countersink and the next corresponds to an angle of forty-tive degrees, the graduations on the dial 19 being positioned and marked accordingly as indicated in Figure 4.

As indicated in Figures 5 and 6, the arc 2 is formed with a plurality of holes 24 extending radially from the front face to the rear face of the arc, the forwards ends of these holes being enlarged as indicated at 24a. In

each one of the holes 24 there is fitted a hollow thimble 25 the rear end portion of which projects beyond the rear face of the arc and is perforated as indicated at 25a, while the forward end is formed with a ange 2Sb engaging snugly in the enlargement 24a of the hole 24. The forward end portion of the thimble 25 accommodates a snugly fitting bush 26 which extends about halfway over the length of the thimble and forms a bearing for a plunger generally indicated at 27. The plunger comprises a forwardly disposed cylindrical portion 27a slidably engaged in the bush 26, and a rearwardly disposed finger-piece 27b projecting freely through the perforation 25a in the rear end of the thimble 25, the portion 27a of the plunger being separated from the finger-piece 27b by means of a collar 27e accommodated within the thimble. A helical compression spring 2S is arranged around the cylindrical portion 27a of the plunger 27 and bears between the inner end of the bush 26 and the collar 27C. Thus, normally, the plunger 27 is maintained by the spring in an extreme rearward position so that the finger-piece 27b projects to a maximum extent from the rear face of the arc, as indicated in the middle part of Figure 5. The cylindrical portion 27a of the plunger is made of such length that, with the plunger in its normal rearmost position, the forward extremity of the portion 27a will lie at a substantial distance inwardly of the forward end of the bush 26 so that this extremity will be, practically speaking, invisible to the patient by being in shadow.

When the finger-piece 27 b is pressed by the practitioner, the plunger 27 will be moved forwardly against the pressure of the spring 28 so that the forward part of the cylindrical portion 27a will pass out of the bush 26, thereby exposing to view the forward extremity of this portion, as indicated at the lower part of Figure 5.

On release of the finger-piece 27b, the spring 28 will act to return the plunger 27 to its normal inoperative position..

In the embodiment illustrated, the thimbles 25, with their bushes 26, are held in their various holes 24 by means of a cover-plate 29 which is secured to the front face of the arc 2, by means of screws 30, the cover-plate being formed with clearance holes 31 which are arranged in axial alignment with the holes 24 in the arc and through which the forward ends of the portions 26a of the plungers 26 can freely pass when any selected one of the plungers is pressed into operative position. A further hole 32 (Figures 2 and 3) is provided in the cover plate 29 and registers with the bore 12 of the spindle 11 so as to let light through the 'fixation point.

Usually the exposed `faceof the cover-plate 29, the exposed parts of the screws and the circular walls of the holes 31 will be treated to give a matt black or other `suitable finish inhibiting reflection of light. The bushes 26 may be made of a dense black material such as ebonite or a synthetic resinous material of a black colour so that the parts of the bores thereof which are exposed when the plungers are in normal retracted position, will not reflect light. Where, however, the bushes 26 are made of a light-reiiecting material such as a metal, the saidpartsof the bores thereof can be treated to give a matt black finish.

To give the necessary contrast, the plungers 27, or the target ends thereof, are made of a white or coloured material, such as a white or coloured form of hard synthetic resin. The possibility` presents itself of making the target ends of-the plungers of different colours.

In Figures l and 2 of the drawings each arm of the arc 2, that is to say, the part extending from the axis about which the spindle 11 is rotatable in the sleeve 1c, to an end of the arc, is shown to be` provided with eighteen plungers 27, making thirty-six plungers for the Whole arc. The plungers' on each arm are arranged at a distance of five degrees apart, this distance being measured from the centre about which the arc is struck,` and the plungers nearest the axis of rotation of the arc, which corresponds to the xation point and constitutes zero, are spaced at a distance of ten degrees apart.

The degrees representing the various distances at which the plungers are situated from zero are marked on the side faces of the arc 2 so that the practitioner can obtain a reading by looking at either one of these faces. To this end, and as illustrated in Figure 6, the side faces of the arc are formed with recesses 33 in which are fitted discs 34 having the gures of degrees suitable inscribed thereon.

In the use of a perimeter constructed as described, the arc 2 will, to start with, usually be positioned to lie in a vertical plane, such position corresponding to zero as indicated by the pointer 20 in relation to the graduations marked on the dial 19. After the patients eye has, by means of the locating protuberance 8, being correctly positioned in relation to the fixation point, the practitioner presses one of the plungers 27 so as to bring the forward extremity of the portion 27a thereof into view and, depending on the response of the patient, takes a reading from the corresponding figure on a side edge of the arc, or releases this plunger and then presses another, and so on until the response made by the patient indicates that a reading should be taken, the practitioner thereby obtaining at least a partial measure of the occular field of the eye under test. lf further exploration is desired, the arc is rotated step-by-step as shown by the pointer 20 in relation to the graduations marked on the dial 19, the plungers 27 being manipulated between each step and a reading taken on each occasion. When the arc has been turned full circle, the practitioner will have obtained a measure, having a substantial degree of accuracy of the entire occular tield of the eye under test.

The arc 2 may carry a lamp or lamps acting to illuminate the target ends of the plungers 27 when these are brought to exposed position, the lamp or lamps being so arranged that the light rays therefrom do not destroy the shadow effect when the plungers are in retractedposition.

Thus. aflamparranged'filr ico'njiniotioiilwithfa suitable# directedfshieldlorf reflector; mayV be fittedE at each?x endg of the arc;

`While in' the 'embodimentilllgistrated,"v tlie arc 2- carries p *extending* from the-front'v-face to the; 'rearlfa'ce' of-the latter, plungers mounted ,forr4 movement infsaid-holes, the forwardextremitiesthereof having `acontrastin g effect withl said 'are -andfmeans Eacting lnormally- -to `maintainy the plungers in aI rear-ward position so' thatfthe forward extremities thereof are `sunlcinV-the holes sufficiently Itobe inIA shadow tandf'substantially invisible" to' the" eye under test when positioned adjacent lthe center of curvaturefof the arc-t andfhavinglitsflinefof; sig-ht iixedona fixation point at a predeterminednosetlocation,with respect to said forward" extremities, and' the plungers being selectively-movableto a-forwardpositi'onls'o as to bring-the' said extremitiesoutofshadow -'andiinto view;` 5 'y 2; A'n ophthalmic perimeterlforuseinf testing eyes-corn prising an arc, aeseriesrofaholes;formed in the arc, said holes being arranged at fixed intervals along thearcand extendingfrom' the" fron-tface to'l the' 'rear face" 'ofir the latter, plungers mounted for axial slidingmovement in said holes, and springs acting normally to maintain the plungers in `a. rearward position so` that the forward extremities thereof are sunk in the holes sufficiently to be in shadow and substantially invisible to the eye under test when positioned adjacent the center of curvature of the arc and having its line of sight fixed on a fixation point at a predetermined offset location with respectpto said forward extremities, and the plungers being individually movable by finger pressure to a forward position so as to bring the forward extremities thereof out of shadow and into view said forward extremities having a contrasting eifect with said arc.

3. An ophthalmic perimeter for use in testing eyes comprising a pedestal, an arc `supported bythe pedestal for rotation about an taxis passing through the center about which the arc is struck, a series of holes formed in and p arranged at xed intervals along the arel and extending from the front face to the rear face of the latter, plungers mounted in said holes for forward and rearward movement, and means acting normally Ito maintain the plungers in a rearward position so that the forward extremities thereof are sunk in the holessuiiiciently to be in shadow, and substantially invisible to the eye under test when positioned adjacent the center of curvature of the arc and having its line of sight xed on a fixation point at a predetermined offset location with respect to ysaid forward extremities, and the plungers being selectively movable to a forward position so as 'to bring said forward extremities out of shadow and into view-said forward extremities having a contrasting 'effect with said,

arc.

4. An opthalmic perimeter for usein -testing eyes comprising a pedestal having a base portion and an upwardly extending arm, an arc, a spindle secure-d lto and extending from the rear face of the arc and arranged in axial alignment with the center about which the yare is struck, said ASpindle being rotatably engaged in the upper end of said upwardly extending arm, a hole extending through the spindle and through which light can pass to the front face of the arc so as to constitute the xa-tion point, a series of holes formed in and arranged Vat fixed intervals along the arc and extending from the frontface to the rear face of the latter, a plunger mounted for axial sliding movement in each hole in the arc, and a spring associated with reach? plunger -andr acting-normallA-y tofmaintainthe plunger in .a rearwardpositionfso@attire rearwardportion of the plunger projectsefromz the rear^facef of" the arc while thev extremityfof 'the forward"portiony ofth'e-'f plunger liesl sunk within the` hole sufliciently to-bev in shadow and" substantiallyl invisible' totheeye-under test atf aV predetermined otfsetf location withjrespect olthe forward i extremities 'ofl the-plungers, .the spring' permitting the plunger to be'movedf" forwardly byfpressurefon"the' projecting rearwardportion oflf'the: plunger so thatfthe extremity'of the forward'portionoffthe plunger isthen brought out of shadow andI into-view atf the frontface of; the; arc the'` forward extremities" ofi'saidplurigershavp ing a contrasting effect with said arc. Y

' 5.`- Anophthalmic perimeter for'use in testingeyes comprising an arc, a series of`hol'sifrmed inf the'farlc,V said holes beingiarranged4 at fixed intervalsf-albngthe'are and opening at the fron-t and frearf faces` of melatten-hollowthimbles arranged in ysaidholes andfhavjing their'forward endsopening at 'the' front face offth'e arc'and theirfrearward end-s formed with perforations, plungers journ-alld foraxial movementin'sa'id thimbles, and sprihgs'acco-m modated `'in the 'thimblesandactirrg normally tojm'aintain the plungers in a rearward position -so thattlie'rearwardy .portions-thereof"project from the rea-r faceqof the varc` while the extremitiesl of 4the forwardport-ionse lie Within the thimbles and are thus-"in shadow? inf relation to the patient; the springs permitting'tlezplurrgersl tofbe selectively moved by finger pressure to a forward position so that the extremities of the forward portions are then exposed at the front face of the arcthe forward extremi-v ties of ysaid plungers having a contrasting arc. f

6. An ophthalmic perimeter for use in testing eyes comeifect with said prising an arc, a series of holes formed in the arc, said holes being arranged at fixed intervals along the arc and` opening lat the front and rear faces of the latter, hollow v thimbles arranged in said holes and having their. forward .ends openng'a-t the front face of the arc and their rearpatient, the springs permitting lthe plungers to be selectively moved by .tinger pressure to a forward position so that the extremities of the forward portions are. then exposed at the front face of the arc, said forward extrem?r ities having a contrasting effect with ysaid arc, and acover .plate acting to hold the thimbles in place Aand `being formed with clearance holes which are arranged in -coincidence with the open forward ends of the thimbles and allow for passage of the forward end portions of the plungers when the latter are moved to their forward positions.

7. An ophthalmic perimeter for use in testing eyes comprising an arc, a fixation point provided on the rare, a

series of holes formed in the arc, said holes being arrangedk at fixed intervals alongthe arc, hollow thimbles -arranged vin sai-d holes and having their forward ends opening at the front face of the arc and their rearward ends formed with perforations, a cover plate secured to the front face `of the arc and having holes in register with'the Vforward open ends of the thimbles, bushes arranged in the forward end portions of the thimbles, plungers having forward end portions engaged for -axial sliding movement in said ybushes and rearward end portions passing freely .through the perforations in the rearward ends of the thimbles, and springs acting on the plungers in such mannerthat the forward' extremities of the forward end portions of the plungers are normally maintained within said bushes v suliciently to be in shadow and substantially invisible `to the eye under test when positioned adjacent the center of curvature of the arc and having its line of sight fixed on j a fixation point at a predetermined offset location with from the perforations in the rearward ends of the thimbles, said springs permitting the projecting rearward por tions of the plungers to be selectively moved towards the thimbles so that the forward extremities of the for-war portions of the plungers are moved through the holes in the cover plate and are thus out of shadow and into View at the front face of the cover plate the forward extremities of said plungers having a contrasting effect with said arc. j,

8. An ophthalmic perimeter for use in testing eyes comprising an arc, a plurality of rows of holes form-ed in the arc, `the holes in each row being arranged at fixed `intervals along the arc and extending from the front face to the rear face of the latter, plungers mounted for axial movement in said holes, and means acting normally to maintain the plungers in such a position that the forward extremities thereof are sunk in the holes suiciently to,

extremities thereof are brought out of shadow and into view at the front face of the are ythe forward extremities of said plungers having a contrasting effect with said arc.

9. An ophthalmic perimeter for use in testing eyes cornprising'an arc, a plurality of plungers axially slidably mounted on said arc and in spaced relation with each other longitudinally of said arc, said plungers having targets on the forward extremities thereof having a contrasting effect with said arc, means acting normally to urge and maintain the :plungers in a rearward position with respect to the front face of said arc so that the targets on said'forward extremities lie rearwardly of said face by an amount sucient to be in shadow and substantially invisible to the eye under test when posiltioned adjacent the center of curvature of the arc and having its line of sight xed on a fixation point at a predetermined offset location with respect to said targets, and the plungers being selectively axially slidable to a forward position with respect to said face so as to bring said targets on said extremities out of shadow and into View.

References Cited in the tile of this patent UNITED STATES PATENTS 

